Shortly after reveille on April 7, 1846, American soldiers with shovels and pickaxes began construction of a permanent installation on the north side of the contested Rio Grande. Brig. Gen. Zachary Taylor, commanding the force sent the previous month from the Nueces River, commanded his troops to rotate out in shifts, leading to a near constant flinging of earth and debris.
The Americans’ forts and palisades were in direct response to a heightened sense of security on their side of the river, which was described by 2nd Lt. Ulysses S. Grant as only “a small muddy stream of probably 150 to 200 yards in width”. Since Taylor’s arrival in late March across from the city of Matamoros, the opposing forces stared warily at each other, waiting for someone to make a move. Engineer George G. Meade wrote to his wife that the Mexican forces across the river “continue to work assiduously, night and day, in putting up batteries all around their town, and to decline all intercourse with us[.]”
The armies were not the only ones paying close attention to each other’s battlements. As the American army arrived on the north side of the Rio Grande and ran up the Stars and Stripes, 2nd Lt. Napoleon J.T. Dana wrote that their flag “was answered by the flags of England, France, and Spain from the consuls’ houses in the city,” as the ambassadors hoped to avoid any crossfire.
As the American soldiers went to work on April 7, they were overseen by Capt. Joseph Mansfield, an engineer officer graduated from West Point in 1822 and the man who Taylor had specifically given the task of building the fortifications.
Mansfield’s final plans, approved by Taylor before the groundbreaking, were in any case, “an ambitious project,” in the words of historian Douglas A. Murphy. “The six-sided earthen fort would have two sides at 150 yards long and the remaining four sides at 125 yards.” Murphy writes. “Where these walls met, Mansfield designed arrow-shaped bastions into which artillery could be placed to counter any angle of attack.” Circumnavigating the entire fort, Mansfield plotted further obstacles, namely a “ditch, 20 feet wide and 8 feet deep,” leading to the complex’s walls, stretching almost ten feet high. When finally finished, Mansfield
intended the fort to house some 500 men.
Officers and enlisted men alike worked on the fort. Twenty-six year old 2nd Lt. Alexander Hays, 7th Infantry and close friends with Ulysses ‘Sam’ Grant, wrote, “Incessantly by day, but with alacrity, our troops piled the pick and shovel, while in view across the plains of Matamoras [sic] squadrons of [Mexican] lancers and masses of infantry performed their evolutions.” The hard work continued for weeks, until by the beginning of May, only small pieces of the fort’s construction remained to be done.
Covering the construction project, Taylor’s engineers also placed a battery of “four 18-pounders”, which, when positioned, “bear directly upon the public square of Matamoras [sic], and within good range for demolishing the town,” Taylor reported to Congress. The cannons’ “object cannot be mistaken by the enemy,” Taylor continued, “and will, I think, effectually restrain him from any enterprises upon our river.”
Though Zachary Taylor wrote confidently back to his superiors in Washington, the impasse along the Rio Grande would soon turn violent, hurling the two nations into full-fledged war.
 The Papers of Ulysses S. Grant, Volume 01: 1837-1861, Edited by John Y. Simon, Southern Illinois University Press, 78.
 The Life and Letters of George Gordon Meade: Vol. 1, (New York: Charles Scribner’s Sons, 1913), 48.
 Monterrey is Ours!: The Mexican War Letters of Lieutenant Dana, 1845-1847, Edited by Robert H. Ferrell, University Press of Kentucky, 1990, 39.
 Douglas A. Murphy, Two Armies on the Rio Grande (College Station: Texas A&M University Press, 2015), 103-104.
 Messages of the President of the United State with the Correspondence, Therewith Communicated, Between the Secretary of War and Other Officers of the Government, on the Subject of the Mexican War (Washington: Wendell and Van Benthuysen, 1848), 133.